How to make a self-cleaning coating that repels all liquid

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What is the best way to keep our screens clean? The first and obvious answer is to keep our hands free of dirt. But there may be another option: self-cleaning coatings created by material scientists.
Recently, Anish Tuteja, a materials researcher at the University of Michigan, developed a clear, smooth layer that repels all liquids and can be applied to any surface. (The research was published in the ACS magazine Applied Materials & Interfaces). There are other repellent coatings, of course, but their abilities are limited. Take, for example, a Teflon tray. "If you put a drop of water on it, it wrinkles, but if you put cooking oil, it will spread," says Tuteja. "That's what happens on most surfaces." The material that his team developed is much more versatile and, as expected, will be available in the coming years.
The Verge spoke with Tuteja about the repellent, how his team develops new materials and what follows for self-cleaning materials.
This interview has been slightly edited for clarity.
As a scientist, you work in "surface science". What is surface science and what are its potential applications?
My group at the University of Michigan works mainly on different types of surfaces that attract or repel different liquids. It is a unique surface that does not exist in nature, but that has many fundamental applications.
In terms of repelling liquids, look at almost any surface around you and you can find an application from screens to tables, chairs and rugs. There is a lot of use for self-cleaning materials and stain-resistant surfaces.
Another area is for heat transport, to improve the condensation on the surfaces. That is relevant to all power plants and nuclear plants in the world. [Editor’s note: Power plants generate steam that turns a turbine to make electricity. The turbine is condensed into water and the process starts again, but the condensers can be inefficient.] It is also useful for cooling, wherever there is a phase change or anything that comes from a vapor to liquid, there is condensation, this would be relevant and would help to save energy.
You said that these surfaces do not exist in nature, but what would be the closest natural material to these properties?
Much of the work in the repellent area has been on textured surfaces. These are rough surfaces that trap air pockets under different liquids. The lotus leaf is the common example: the drops of water will enter and bounce.
That repels water, but not other materials such as oil and alcohol. Take your non-stick Teflon tray, for example. If you put a drop of water, it accumulates, but if you put cooking oil, it will spread. That is what happens on most surfaces. There are no smooth surfaces that repel everything.
And its coating is a smooth surface that can repel liquids. You call it "omniphobic." What does that mean exactly?
The surface is resistant to moisture. Our definition of "omniphobic" coating means that the liquid will not spread. Then different liquids such as water, oils and alcohol will not spread on the surface. In addition, liquid droplets can slide off the surface very quickly, which makes them very easy to clean. Therefore, if you have a camera lens with the coating, you can tilt the surface and the water or oil will slide out.
I was interested in how you came up with the idea. Instead of mixing materials, it involved a lot of calculations to see what could work together, right?
Absolutely. To make a repellent, you usually take a material called filler and a polymer binder and mix them. The polymer binder provides durability and the filler provides these repellent properties. Therefore, you might think that if you take the most durable filler and the most durable polymer and mix them, that would lead to the most durable surface.
That is not the case. What is really important is how well these components mix and interact, what we call "miscibility". Instead of mixing and combining, we made our own calculations of the properties of many substances to find the best range. Mathematically we came up with formulations that could work well together, and that means that we are not limited to a single formulation. It allows us to see different polymers and different fillings and discover which are more likely to have similar properties. It allows us to predict what the best substances might be.
How does the coating feel? And how long would it last? Let's say I use the coating on my iPhone, when would I have to reapply it?
It is quite thin and it is difficult. It is based on urethane, which is an elastic material, so it feels like a rigid rubber layer. As for how long it will last, it depends on the exact formulation, but we expect something of the order of a year.
How about getting these in the market? When will that happen?
We are actively working on the commercialization of surfaces like these. We are working with a startup, Hygratek, which I co-founded, to launch it in the next one or two years.
The main challenge we are trying to address is the durability of the coating and getting it to have a good feeling. And, of course, you want to make sure that the cost is not too high. We are trying to find an optimal formulation, and not just one, to see which would be the most competitive in terms of costs.
Do we know for sure that this will not have any effect on health?
We are testing The molecule used in this document contains fluorine, and there is a large amount of data we have on how it is not toxic. But there are things in progress that we must resolve. And this particular molecule is still available only in relatively small quantities, so we are also looking for other formulations that are not toxic and are also based on more commercially available materials, different combinations of polymers.
What else are you working? What else is being developed in the area of ​​surface science?
We are also working on omniphobic coatings that repel or kill microbes and materials that are phobic. In these, the ice does not adhere, so it would be very useful for airstrips of aircraft and power lines and wind turbines. We are also making dust resistant surfaces.
In the area of ​​surfaces that attract water, we are creating surfaces that will attract water but repel oil. None of that exists in nature, where it can cause oil to grow but water to spread on the surface. These membranes could be used to clean oil spills, for example.


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